1. Technical Field
The invention concerns a method of producing a joint between the end of a helically corrugated metal tube and a coupling.
2. Description of the Background Art
There are many ways of connecting metal tubes to each other or producing a joint between a metal tube and a coupling. Thus it is commonplace to solder or to weld or to screw the cited components to each other.
Joining thin-walled tubes to each other or to a coupling is problematic since it is difficult to screw or weld them together because of the thin wall thickness, and soldering can only be used on a few metals.
Even more complicated is joining a thin-walled helically corrugated metal tube to a coupling.
It is known from CH-PS 589 249 to roll the end of a corrugated metal tube against the inner surface of a flange, which flattens the corrugation. The high pressure created during the rolling process produces a tight pressure connection between the previously corrugated metal tube and the metal flange. This type of joint requires expensive equipment in the assembly area and presupposes thick-walled preformed parts.
Another kind of joint for corrugated metal tubes is described in DE-PS 33 02 450. A support bushing is screwed onto the end of a corrugated tube and a pipe socket is screwed into the end of the corrugated tube. The sealing is provided in that the clear width of the support bushing increases toward the end and/or the outside diameter of the pipe socket decreases toward the end. When the pipe socket is screwed into the end of the corrugated tube, which has been adapted for the inside contour of the outer bushing by means of a molding tool, the corrugated tube becomes sealed between the pipe socket and the support bushing.
A connecting valve for helically corrugated metal tubes is known from DE-OS 40 27 818 and comprises an outer bushing that is screwed onto the end of the corrugated tube, and a smooth tube neck which protrudes from the end of the corrugated tube. The smooth tube neck has an internal thread into which a tube connection piece is screwed. A stepped end of the tube connection piece penetrates into the corrugated tube. The corrugation at the end of the corrugated tube is crushed when the tube connection piece is screwed in. The sealing is provided by inserting a graphite sealing strip into the final corrugations, which becomes deformed by the crushed corrugations and is pressed against the inner wall of the outer bushing and the stepped end of the pipe socket penetrating into the end of the corrugated tube.
A sealant packing for corrugated tubes is known from DE-A-3 341 297; it comprises two bushings that fit into each other and can be moved with respect to each other, between which an annular space for receiving a sealing material is formed around the corrugated tube. A corrugated tube sleeve which fits the inside of the sealing area is provided. Graphite is suggested as the sealing material.
An arrangement for joining the end of a corrugated tube to a coupling is known from EP 0 775 865 B2, where a support ring is screwed into the end of the corrugated tube and its end protrudes from said corrugated tube. A thrust collar is screwed onto the end of the corrugated tube until the end of said corrugated tube protrudes. The coupling and the thrust collar form a sealed chamber in which a graphite sealant ring is placed so that it is compressed by the axial pressure effect of the thrust collar and the coupling.